1. Field of the Invention
The present invention relates to a novel colorant compound, an ink comprising the compound, and an ink tank, a recording unit, a recording apparatus and a recording process comprising or using this ink.
2. Related Background Art
With the life-style change due to the progress of science and technology, colorants have come to be used not only for dying or coloring various materials such as fibers, plastics and leather heretofore, but also in various industrial fields making good use of their properties of recording or displaying information. In particular, with the rapid spread of personal computers in recent years, the hard copy technology typified by ink-jet printing has been advanced for recording characters and image information outputted from the computers.
Water-soluble dyes are generally used as colorants for ink-jet inks. However, recorded images formed by inks containing water-soluble dyes have been poor in water fastness and involved a problem that bleeding of dyes easily occurs at recorded areas when water is spilled thereon, though improvement has been gradually made. On the contrary, images excellent in water fastness can be formed by inks using a pigment as a colorant, so that a great number of recording liquids (inks) obtained by dispersing a pigment in an aqueous medium have been developed for the purpose of improving the water fastness of ink images formed (see, for example, Japanese Patent Application Laid-Open Nos. 2003-286433, 2003-306624, 2003-327885 and 2003-335986). However, images formed by printing with inks using a pigment as a colorant are excellent in water fastness, but have involved another problem that color reproduction quality and transparency of the images are poor compared with the case of inks using dyes because they tend to cause light scattering by the influence of pigment particles.
In order to solve these problems and make it possible to form images satisfying water fastness while retaining excellent color reproducibility and transparency in images obtained by using water-soluble dyes as colorants for inks, processes for obtaining an ink by coloring a water-dispersible resin with an oil-soluble dye have been proposed (see, for example, Japanese Patent Application Laid-Open Nos. 2001-11347 and 2001-240763).
However, the oil-soluble dyes heretofore used in the above-described processes are not sufficient in hue as a magenta color, and there is thus a strong demand for development of colorants having an excellent magenta color for the purpose of forming images of higher image quality.
Here, xanthene dyes and pigments are known as magenta colorants. Since the xanthene colorants generally have 2 absorption bands (x-band and y-band) in the visible region, the complementary colors of the x-band on a longer wavelength side and the y-band on a shorter wavelength side are observed as a hue. Therefore, a xanthene colorant having an ideal magenta color is required to be such that both absorption bands overlap with each other on the absorption band of the complementary color of a magenta color. Examples of such xanthene colorants include C.I. Acid Red 289. Since such a colorant is water-soluble, however, it involves a problem that the water fastness of an image formed with an ink containing the colorant is poor.
It has heretofore been reported to develop colorants having an analogous structure to C.I. Acid Red 289. For example, there is disclosed a process for obtaining a water-soluble polymeric dye by chlorosulfonating C.I. Acid Red 289 and then sulfonamidating the resultant product with a water-soluble polymeric quaternary ammonium salt, and ink solutions using such an ink (see Japanese Patent Registration No. 3263524). A process for producing an ink-jet recording liquid with a C.I. Acid Red 289 analogue is also disclosed (see, for example, Japanese Patent Application Laid-Open No. H09-255882). Since these colorants are water-soluble, however, the water fastness of images formed by such inks is not sufficient, and these colorants are inferior to C.I. Acid Red 289 in point of a hue as a magenta color.
As described above, no colorant having a good magenta color and high oil-solubility, i.e., high solubility in organic solvents, particularly, nonpolar solvents has been known to date.